Programming device for roll feed brake



Feb. 26, 1963 c. M. wuc;

PROGRAMMING DEVICE FOR ROLL FEED BRAKE 6 Sheets-Sheet 1 Filed May 51,1960 l H nl I I m WI I fzuazab or. 6%esfe2" 5% MM Feb. 26, 1963 c. M.wne v 3,078,734

PROGRAMMING DEVICE FOR ROLL FEED BRAKE Filed May 31, 1960 6 Sheets-Sheet2 Jim @2360)".

Feb. 26, 1963 c. M. WllG PROGRAMMING DEVICE FOR ROLL FEED BRAKE 6Sheets-Sheet 5 Filed May 31, 1960 KHP H \Ill lllllll '4' iizuerz Feb. 261963 c. M. wue 3,078,734

PROGRAMMING DEVICE FOR ROLL FEED BRAKE I Filed May 31, 1960 6Sheets-Sheet 4 llll ll y 5 Who h;

Feb. 26, 1963 c. M. wile 3,

PROGRAMMING DEVICE FOR ROLL FEED BRAKE Filed May 31, 1960 6 Sheets-Sheet5 BEIVfi IMPL D OFF FEED P05177001 *g Max gag? Feb. 26, 1963 c. M. wue

PROGRAMMING DEVICE FOR ROLL FEED BRAKE 6 Sheets-Sheet 6 Filed May 31,1960 g mwmdwf United States Patent Ofi 7 3,078,734 Fatented Felt. 26,1963 ice nois

Filed May 31, 1960, Ser. No. 32,642 Claims. (Cl. 74-130) The inventionrelates to material feeding mechanism for feeding metal and othermaterial in continuous strip form and has reference in particular toprogramming apparatus for such feeding mechanism for controlling thebraking pressures applied to the feed rolls whereby to insure properfunctioning of the feed roll drive mechanism.

In the feeding of metal strip material for cutting, punching and similaroperations, it is conventional procedure to employ coacting feed rollswhich are preferably actuated intermittently from a main drive shaftthrough a ratchet or over-running type of clutch. The feed rolls areaccelerated from an idle position to maximum speed during the operativestroke of a reciprocating rack and braking means are employed to assistin decelerating the rolls and in causing the rolls to stop at the end ofthe operative stroke and before the inoperative stroke of the rackbegins. It is necessary to apply braking pressures to such intermittenttype of drives since otherwise the inertia of the rotating parts wouldcause the feed rolls to overrun and such action would, of course,destroy the accuracy of the measured feed lengths.

An object of the invention is to provide programming apparatus forfriction brake means and which may be incorporated in intermittent drivemechanism of the type described for controlling the braking pressuresapplied to the feed rolls.

A further object of the invention resides in the provision ofprogramming apparatus for friction braking mechanism such as may beapplied to intermittently op erating feed rolls and which will actuatethe friction brake mechanism automatically and in predetermined timedrelation to the main driving shaft for the said feed rolls.

Another and more specific object of the invention is to provide aprogramming cam for controlling friction brake mechanism and wherein thecam can be adjustably .positioned on the main drive shaft for the feedrolls whereby the entire programming action can be varied with respectto the feeding operation of the feed rolls.

A further object is to provide improved and highly efficient frictionbrake mechanism for the feed rolls of an intermittent strip feedingmachine and to further provide programming apparatus in combinationtherewith for automatically actuating in a controlled manner the saidfriction brake mechanism.

With these and various other objects in view, the invention may consistof certain novel features of construction and operation, as will be morefully described and particularly pointed out in the specification,drawings and claims appended thereto.

In the drawings which illustrate an embodiment of the device and whereinlike reference characters are used to designate like parts-- FIGURE 1 isan end elevational view of a continuous strip feeding mechanism of theintermittent type, the same incorporating the improved friction brakingapparatus and programming means of the invention;

FIGURE 2 is a fragmentary end elevational view showing the improvedfriction braking apparatus and programming means in operative relationon the continuous strip feeding mechanism;

FIGURE 3 is a fragmentary front elevational view of the friction brakingapparatus and programming means as shown in FIGURE 2;

FIGURE 4 is a vertical sectional view taken longitudinally of thefriction braking apparatus and programming means substantially alongline 44 of FIGURE 2;

FIGURE 5 is a fragmentary sectional view on an enlarged scaleillustrating in detail the operating structure for effecting theapplication and release of the braking mechanism;

FIGURE 6 is :a fragmentary end elevational view of the structureillustrated in FIGURE 5, with parts being shown in section;

FIGURE 7 is a fragmentary sectional view taken substantially along line7--7 of FIGURE 6;

FIGURE 8 is a sectional view showing a type of overrunning clutch suchas may be employed in the intermittent feeding mechanism of thecontinuous strip feeding machine;

FIGURE 9 is an end elevational view of the programming cam of theinvention;

FIGURE 10 is a top plan view of the programming cam showing the indiciafor predetermining the adjustment of the cam on its drive shaft; and

FIGURE 11 is a schematic view diagrammatically illustrating a braketiming curve.

Referring in particular to FIGURES l and 3 of the drawings wherein theinvention is illustrated as applied to a continuous strip feedingmachine of the intermittently operating type, it will be observed thatthe machine generally designated 20 includes a frame consisting of abase portion 21, side walls 22 and 23, and a top wall 24. The framejournals the main drive shaft 26, and the top wall supports the feedingrolls 27 and 28 which are, in turn, suitably journalled by the supports36 as best shown in FIGURE 3. The feeding rolls are geared to rotate inunison and with the strip material located between and gripped by thefeed rolls, said strip material will be fed in the desired manner as therolls are caused to rotate.

The intermittent feeding mechanism of FIGURE 1 is characterized by afeeding action for the major portion of the cycle and by a quick return.The main shaft 26 is provided with a collar 31 having a stud shaft 32for oscillating the member 33. Oscillating movement of member 33 in turnproduces reciprocating motion of the rack arm 34 which drives the lowerfeed roll 28 through the overrunning clutch, indicated generally bynumeral 35 in FIGURE 8. The stud shaft 32 coacts with a block 36 whichrides within the passageway 37 provided by the member 33. Said member 33is journalled for oscillating movement by the eccentric 3% located onthe shaft 49. Accordingly, the pivot axis of the oscillating member 33is variable, depending on the rotated position of the shaft 40.

The rack arm 34 has pivotal connection as at 41 with the member 33through the instrumentality of a block 42 which is adapted to ride in aguideway 43 provided by member 33. The said block is suitably threadedto the threaded adjusting rod 44 which is journalled at its opposite endby the part 45. By applying a suitable tool to the squared end 46 of theadjusting rod, the said rod can be rotated in either direction to changethe position of the block 42 and thus the pivot axis of the rack arm 34.However, for any particular basic stroke as determined by the rotatedposition of the adjusting rod 44, it is possible to vary the length ofthe stroke Within narrow limits by adjusting the position of theeccentric 38.

The rack arm 34 has meshing relation with a pinion 59, the said pinionhaving trunnions which support the body portion of the rack and thepinion housing 51. The pinion 50 is located on the lower feed roll shaft52, and the pinion-is free to rotate on said shaft. The trunnionsprovide an annular casing 53, FIGURE 8, within which is located thestructure of the overrunning clutch as generally identified by thenumeral 35. Said clutch structure includes an inside body member 54which is suitably keyed at 55 to the shaft 52. The member 54 provides aplurality of hardened steel inserts 56 on which are supported thegripping rollers or balls 57, the same being backed by the coil springs53. Accordingly, a one way clutch is provided whereby reciprocatingstrokes of the rack 34 in one direction only will be transmitted to thefeed rolls. The action of the oscillating arm 33 on the rack 34 is toproduce an operative stroke in the downward direction and which mayoccupy approximately 230 degrees of each revolution of the main driveshaft 26. Since the shaft and thus the collar 31 are rotating in aclockwise direction, it will be seen that this downward operative strokeof the rack for rotating the feeding rolls will be relatively slow ascompared to the upward inoperative stroke of the rack which isrelatively fast. Thus a long feeding stroke with a quick return isachieved with resulting greater accuracy in the measured lengths as fedby the rolls. Reference is made to the Wiig Patent 2,756,994 grantedJuly 31, 1956 for a more particular description of the intermittentfeeding mechanism of FIGURE 1.

In accordance with the invention the lower feed roll shaft 52 isprovided with friction braking means for braking the feed rolls toprevent overrun and thereby maintain greater accuracy in the measuredfeed lengths of the strip material fed by the machine. The frictionbraking mechanism, as best shown in FIGURE 4, includes a pair of outerhousing members 69 and 61, and a pair of inner members 62 and 63, allconcentrically disposed with respect to shaft 52. The members 69, 61, 62and 63 comprise the static elements of the pres ent brake device, sincethey do not rotate, whereas the rotating or dynamic element is providedby the center member 64 having the brake discs 65 suitably securedthereto. The center member 64 is mounted on and secured to the hub part66, which is in turn keyed at 67 to the shaft 52. The center member 64-is generally termed the brake disc, whereas the inner members 62 and 63comprise pressure plates or brake shoes, since they contact the brakediscs 65 and apply pressure thereto to brake the rotating action of theshaft 52. The outer member 60 and 61 provide blower housings for thepresent friction brake mechanism, and it will be observed from FIGURE 2that the outer housings 60 and 61 are, respectively, associated with thecentrifugal blowers designated by the numerals 71 and 72. An electricmotor such as 73 is associated with each of the centrifugal blowers andair under pressure is supplied to within the present brake structure forcooling the operating parts thereof.

The mounting of the outer housing members 60 and 1 on the pressureplates 62 and 63, and the mounting of the pressure plates on the frameof the feeding machine is unique, and the same contributes materially tothe successful operation of the present brake device. For said mountingpurposes the pressure plates are each provided with spaced extensionssuch as '74 and 7S, respectively, the same being located at the top andat the bottom of each pressure plate, as best shown in FKGURES 2 and 3.The pair of extensions 74- at the top of pressure plate 62 have securedthereto the flexible metal strap '76 FIGURE 3 and the pair of extensions75 at the bottom of the same pressure plate have secured thereto theflexible metal strap 77. In each case the securing means includes a bolt'78 and nuts 7?, and which resiliently retain the parts in securedrelation by means of the interposed resilient washer 3i) of rubber orother similar material, see FIGURE 4. Each flexible metal strap isfastened to the frame of the machine by screws 81 which are locatedcentrally of the metal strap. said flexible metal straps provide torqueanchoring connections which permit limited movement of the pressureplate toward and from the brake disc 64. In a similar manner pressureplate 63, having extensions 75, is anchored to the machine frame by theflexible metal'straps 82 and 83 at the top and bottom, respectively, ofthe plate. With the pressure plates of the present braking device thusflexibly supported on the machine frame, it will be seen that the outerhousings 6G and 61 are in turn supported on said plates by the bolts 85.Said bolts are threaded at each end, and by means of the nuts 86 and ashoulder provided by the bolts at each end thereof, the said outerhousings are so cured together to form a unit, and said housings aremaintained in precise spaced relation with each other. The bolts passthrough openings 87 in the pressure plates. as best shown in FIGURE 4.It will also be understood that said pressure plates are normally heldin spaced apart relation by the coil springs 88 located on the bolts hi)and which are suitably fastened to the outer housings 69 by the nut 91.Thus, when the parts of the brake assume their normal positions, thepressure plates 62 and 63 are spaced from the brake disc 64 a sufficientdistance to free the disc, and accordingly, the brake is inoperative inthat no braking pressure is applied to the rotating shaft 52-.

The structure for applying the brake consists of camming mechanism whicheffects a separating action between pressure plate 63 and the outerhousing member 61. The pressure plate 63 is moved to the left, FIGURES 4and 5, into frictional contact with the brake disc 64 and simultaneouslyand to substantially an equal extent the outer housing 61 is moved tothe right. Since the outer houslogs are connected by the bolts 85 formovement as a unit, it will be seen that the outer housing 60 is alsomoved to the right, and in so moving it forces the pressure plate 62into frictional contact with the disc 64.

The hub member 92, as best shown in FIGURES 5 and 7, is fixedly securedto the outer housing 61 by the bolts 93, and said hub member is recessedto provide the center support 94 which is cored to form the throughpassage 95. The exterior of the hub member 92 is recessed at 96providing a circular well in concentric relation with the cored passage95. The ball bearing structure fixedly secured to the center support 24includes the inner ball bearing race 97, the outer ball bearing race 98and the plurality of balls 1%, having location between and engaging theinner and outer races. The outer sleeve 101 is fixed to the outer races98 and said sleeve projects to the left of the ball bearing structurewhere the same is recessed to receive, as by a press fit, the cam ring102. The outer races 98, the sleeve 1G1, and the cam ring 102 comprise aunit which is thus journalled to rotate on the center support E4. Forthis purpose the sleeve is integral with a laterally extending arm 163as clearly evident from FiGURE 6, and which is actuated by a programmingcam as will be presently explained in detail. A pin 99 located inaligned openings in the sleeve and cam ring prevents relative rotationof the elements.

The cam ring 162 is one member of an actuating device which includes asecond similar cam ring 134 and camming balls 105 located between therings and retained by the center disc 186. As best shown in FIGURE 7each cam ring is recessed or grooved at 107 for ring 162, and at 1 28for ring 194. Thus a pair of grooves are provided for each of the balls105 and in order to produce the desired braking action by the pressureplates, the recesses 167 and 168 for each ball are opposed, with eachrecess having a varying depth in a circular direction and wherein theaxis of the cam rings forms the center. In the present embodiment threeballs 105 are employed, see FIGURE 6, and which are spaced around thecam rings at degree intervals. Also in accordance with the invention, itwill be observed that the three recesses 197 for cam ring 102. each havea maximum depth at the right hand side and a minimum depth on the leftside. The three recesses 198 for cam ring 164 are reversed, having amaximum depth on the left and a minimum depth on the right. When one camring such as 102 is rotated to align the areas of minimum depth, the camrings are forced to move'farther apart and this separating movement ofthe cam rings is imparted through the connecting elements to thepressure plates to cause the plates to move toward each other and thusfrictionally engage the respective sides of the brake disc.

Whereas the cam ring 102 is adapted to be rotated by the arm 103, thecam ring 1tl4- does not rotate, since it is fixed in position on thepressure plate 63 by the pin or stud 109. A shaft 110 is locatedcentrally of the hub 92, being disposed within the passage 95 andprojecting beyond the hub member 92. The inner end of shaft 110 isthreaded into the collar 112. The cam ring 104 is fixed to the collar112 as by having a press fit, and the serrations 113 assure that theparts will not rotate relative to one another. This threaded inner endof shaft 110 is recessed to receive the rivet 114, the rounded head ofwhich is located in contact with the pressure plate 63. Said ,pressureplate 63 provides an arcuate depression 115 for accommodating the rivethead.

The adjusting ring 116 is keyed at 117 to the projecting end of shaft110 and the ring is held to the shaft by, the nut 118. Part of theexterior of the adjusting ring is knurled as at 119 with the remainderbeing formed with axial grooves providing the serrations 120 which coactwith the indexing levers 121 as best shown in FIGURE 6. The :coile/clspring elements 122 maintain the levers in 'a selected groove. When itis desired to adjust the brake elements in the event of wear of thebrake disc or for other reasons, the levers are released and theadjusting ring is rotated to thus rotate shaft 110 and thread the samefarther onto the collar 112. This will move the rivet to the 'left(FIGURE 5) and the same will decrease the spacing between the pressureplates. When a desired ad justment has been eifected, the levers 121 arereturned to an aligned groove inthe serrated part 120 of the adjustingring and the parts are thus effectively held in adjusted position. v

The programming cam 124, FIGURES 9 and 10, is formed with a cam race 125havivng a contour of a particular. design and. .which programs thebraking action of the brake device. Said cam 124 is fixed to the shaft126which is journalled in the frame of the feeding machine. The endlessbelt or chain 127 provides the drive for shaft 126 and it will beobserved that said chain passes over the sprockets 128 located on theshafts, respectively. The rear hub 130 of the programming cam is splitas at 131 and the said hub is recessed for receiving the end of shaft126. By means of the securing bolt 132 it is possible to position theprogramming cam on the shaft in a desired adjusted position and whichcan be varied within limits so as to vary the entire program for thebrake device with respect to the intermittent feeding of the feed rolls.The adjusted position of the programming cam 124 on shaft 126 isvisually indicated by the pointer 133 which is located with respect tothe indicia 134 on the cam. A collar 135 is located on the extendingshaft 136 of the cam and the said collar is held in place by the nut137. A strut or tension bar 138 is secured at 139 to the collar and thesaid strut at its opposite end is suitably secured at 140 to the hubmember 92 through the connecting part 141.

The actuating rod 142 for the programming cam joins the lever arm 103with the cam race 125'. For this purpose the rod carries at its cam endthe roller 143' having location within the race and which is fixed tothe rod by the securing nut 144. The upper or lever end of the actuatingrod extends through the lever arm 1% and projects beyond the same toreceive on its extending end the coil spring 145. The upper end of thesaid coil spring seats on the washer 146 which is held to the threadedend of the actuating rod by the nut 14-7. The lower end of the coilspring seats on the washer 148 having an undersurface which is arcuatelyrecessed at 150. The arcuate recess assists in connecting the rod withthe lever through a ball and socket joint which is provided by theseparate ball sections 151 and 152. The ball section 151 has contactwith washer 148, being seated within the arcuate recess 15%. The ballsection 152 in a similar manner contacts the part 153 formed integralwith the rod 142 and which is received in the arcuate recess 154 forseating the ball section. The end of lever 103 is pointed forassociation with the on and off indicia located on the hub member 92.

By way of explanation and not to be considered as limiting, it may beexplainied that the programming cam selected for illustration isprovided with a contour which actuates the rod 102 a total distance ofapproximately five-eighths of an inch. It is necessary for the actuatingrod to move about one-half of this distance before the brakes areapplied and for the next five-sixteenths of movement of the rod, brakeaction is applied to the shaft 52 in a manner which progressivelyincreases in intensity until full brake pressure is attained. Inreferring to the brake timing curve as shown in FIGURE 11, it will beseen that the brake device is initially applied when approximatelyone-half of the 230 degree feed cycle has taken place. ,At this point inthe feed cycle, the rotation of the feed rolls is a maximum. For theremainder of the feeding cycle the feed rolls are gradually decelerateduntil rotation is stopped at the end of the feeding stroke. As evidentfrom the brake timing curve of FIGURE 11 the programming cam graduallyapplies a braking action to shaft 52 until full braking pressures areeffected just before the ending of the feeding cycle. Full brakepressure continues for about ten degrees after the feeding cycle hasended and then for about thirty degrees the brakes are graduallyreleased.

The present device is characterized by eflicient and positive brakepressure and which is applied and released with the minimum of movementof the actuating rod. When said rod is moved upwardly the brake isreleased and when moved downwardly the brake is applied. The coil springis an essential element as regards the actuating rod 142 since thecompressive force of the said coil spring is effective in actuating thecamrning mechanism to apply full brake pressures. The programming camwill move the rod 142 for a tot-a1 of five-eighths of an inch. For thefirst five sixteenths of this movement the lever 103 is moved from oif"to an on position. Accordingly the camming mechanism Will produce anapplication of the brakes. The next five sixteenths of down movement ofthe rod 142 Will take place by compressing the coil spring 145 sincefurther movement of lever 1613 is not possible. Thus the spring ineffect locks the camming mechanism in operative position since themechanism is resiliently held in a manner preventing any separation ofthe cam rings. This eventually results in full application of the brakesand which is clearly shown in the diagram of FIGURE 11 wherein fullbrake pressure exists from about 215 degrees to 240 degrees. Upon upwardmovement of the rod 142 the spring tension is first released and thenthe lever 103- is moved to the off position.

What is claimed is:

1. In a machine of the class described, the combination with a feed rolldrive shaft, of a reciprocating rack and connections between the rackand the drive shaft whereby the drive shaft is rotated intermittently,the improvement which includes a brake device in associated relationwith the feed roll drive shaft, said brake device including a centerbrake disc fixed to rotate with the feed roll drive shaft, anon-rotatable pressure plate on each side of the center brake disc andmounted for axial movement to and from the brake disc, means normallymaintaining the pressure plates out of frictional contact with thecenter brake disc, camming mechanism including a hub member operativelyconnected to one pressure plate and journal-ling a cam ring, a secondcam ring fixed to the other pressure plate, camming balls between thesaid cam rings and having contact therewith, a lever arm fixed to thejournalled cam ring for rotating the same relative to the other cam ringwhereby to cause the cam rings to separate and effect movement of eachpressure plate towards the other for frietionally engaging the centerbrake disc, a programming cam having rotation in timed relation with thereciprocating movements of the rack, and an actuating rod operativelyconnecting the programming earn with said lever arm for effectingoscillating movement of the lever arm.

2. In a machine of the character as defined by claim 1.,Wh616ll'1 thecam rings are each provided with recesses for receiving the carnmingballs respectively, and wherein the recesses vary in depth in a mannerwhich is reverse to that of the recess opposite thereto, wherebyrotation of one cam ring relative to the other produces a carnmingaction causing the can rings to separate or move towards each otherdepending on the direction of rotation.

3. In a friction brake device, the combination with a rotating driveshaft, of a center brake disc fixed to rotate with the drive shaft, apressure plate located on each side of the center brake disc forfr-ictionally contacting the said brake disc, resilient means normallymaintaining the pressure plates out of frictional contact with thecenter brake disc, a housing member on each side of the center brakedisc and having enclosing relation with the pressure plate on its side,connecting bolts joining the housing members to form a unitary structureand said bolts passing through openings in the pressure plates andfixedly maintaining the housing members in predetermined spacedrelation, camming mechanism including a hub member fixed to one housingmember and journalling a cam ring, a second cam ring fixed to thepressure plate enclosed by the said one housing member, means locatedbetween the cam rings for producing a camming action when the journalledcam ring is rotated relative to the other cam ring to thereby cause thecam rings to separate or move toward each other depending on thedirection of rotation, and means for oscillating the journalled cam ringto actuate the camming mechanism and etfect movement of the pressureplates towards and from the center disc.

4. In a friction brake device, the combination with a feeding machine,of a feed roll drive shaft journalled by said machine, a center brakedisk fixed to rotate with the drive shaft, a pressure plate located oneach side of the center brake disk for frictionally contacting the saidbrake disk, flexible metal straps fixed to each pressure plate and tothe feeding machine for non-rotatably mounting the pressure plates onthe machine in '1 manner permitting limited movement of each plate in anaxial direction, a housing member on each side of the center brake diskand having enclosing relation with the pressure plate on its side,connecting bolts joining the housings to form a unitary structure andsaid bolts passing through openings in the pressure plates to therebyfixedly maintain the housing members in predetermined spaced relation,camming mechanism for effecting movement of the pressure plates in anaxial direction, whereby braking action is applied to the drive shaftwhen the pressure plates are moved into frictional contact with thebrake disk and is released when the pressure plates are moved out offrictional contact with the brake disk, said camming mechanism includinga hub member fixed to one housing member and journallin a cam ring, asecond cam ring fixed to and carried by the pressure plate which isenclosed by the said one housing member, and earn elements between thecam rings and in Contact therewith whereby to cause axial movement ofthe cam rings upon rotation of the journalled earn ring relative to theother ring, said axial movement of the cam rings producing axialmovement of the pressure plates respectively to effect said brakingaction and release tiereof.

5. In a friction brake device as defined by claim 4, additionaliyincluding a collar disposed concentrically and extending axially throughthe said cam rings, an adjusting shaft located centrally of the hubmember and extending axially through the collar, said adjusting shafthaving threaded relation with said collar, and said adjusting shafthaving contact with the pressure plate to which the second cam ring isfixed.

References t'lited in the file of this patent UNITED STATES PATENTS531,680 Hannurn Jan. 1, 1895 546,631 White Sept. 17, 1895 2,105,867Stewart Jan. 18, 1938 2,262,708 Lambert Nov. 11, 1941 2,456,990 Johnsonet al Apr. 12, 1949 2,594,708 Amiet Apr. 29, 1952 2,756,994 Wiig July31, 1956 2,758,837 Littell et al Aug. 14, 1956

1. IN A MACHINE OF THE CLASS DESCRIBED, THE COMBINATION WITH A FEED ROLLDRIVE SHAFT, OF A RECIPROCATING RACK AND CONNECTIONS BETWEEN THE RACKAND THE DRIVE SHAFT WHEREBY THE DRIVE SHAFT IS ROTATED INTERMITTENTLY,THE IMPROVEMENT WHICH INCLUDES A BRAKE DEVICE IN ASSOCIATED RELATIONWITH THE FEED ROLL DRIVE SHAFT, SAID BRAKE DEVICE INCLUDING A CENTERBRAKE DISC FIXED TO ROTATE WITH THE FEED ROLL DRIVE SHAFT, ANON-ROTATABLE PRESSURE PLATE ON EACH SIDE OF THE CENTER BRAKE DISC ANDMOUNTED FOR AXIAL MOVEMENT TO AND FROM THE BRAKE DISC, MEANS NORMALLYMAINTAINING THE PRESSURE PLATES OUT OF FRICTIONAL CONTACT WITH THECENTER BRAKE DISC, CAMMING MECHANISM INCLUDING A HUB MEMBER OPERATIVELYCONNECTED TO ONE PRESSURE PLATE AND JOURNALLING A CAM RING, A SECOND CAMRING FIXED TO THE OTHER PRESSURE PLATE, CAMMING BALLS BETWEEN THE SAIDCAM RINGS AND HAVING CONTACT THEREWITH, A LEVER ARM FIXED TO THEJOURNALLED CAM RING FOR ROTATING THE SAME RELATIVE TO THE OTHER CAM RINGWHEREBY TO CAUSE THE CAM RINGS TO SEPARATE AND EFFECT MOVEMENT OF EACHPRESSURE PLATE TOWARDS THE OTHER FOR FRICTIONALLY ENGAGING THE CENTERBRAKE DISC, A PROGRAMMING CAM HAVING ROTATION IN TIMED RELATION WITH THERECIPROCATING MOVEMENTS OF THE RACK, AND AN ACTUATING ROD OPERATIVELYCONNECTING THE PROGRAMMING CAM WITH SAID LEVER ARM FOR EFFECTINGOSCILLATING MOVEMENT OF THE LEVER ARM.